2026 ICD-10-CM Diagnosis Code K31.6Fistula of stomach and duodenum

ICD-10-CM Codes›K00–K95›K20-K31›K31

ICD-10-CM K31.6
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

K31.6 is a billable ICD-10-CM diagnosis code for fistula of stomach and duodenum. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 391 through 392. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified and unspecified disorders of stomach and duodenum.

Code Identity

ICD-10-CM Code
K31.6
Billable Status
Yes — Valid for Submission
Code Describes
Fistula of stomach and duodenum
Short Description
Fistula of stomach and duodenum
Same as the full description in the CMS dataset.
Parent Code
K31
Other diseases of stomach and duodenum

Code Classification

ChapterK00–K95Diseases of the digestive system
SectionK20-K31Diseases of esophagus, stomach and duodenum
CategoryK31Other diseases of stomach and duodenum
This CodeK31.6Fistula of stomach and duodenum

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired gastric fistula
  • Aortic fistula
  • Aortointestinal fistula
  • Duodenal fistula
  • Duodenal stump fistula
  • Duodenoaortic fistula
  • Duodenocolic fistula
  • Duodenoenteric fistula
  • Duodenorenal fistula
  • Enterocolic fistula
  • Enterocutaneous fistula
  • Enteroenteric fistula
  • Esophagoenteric fistula
  • External duodenal fistula
  • External gastric fistula
  • External gastrointestinal fistula
  • External small bowel fistula
  • Gastric fistula
  • Gastrocolic fistula
  • Gastroduodenal disorder
  • Gastroduodenal fistula
  • Gastrointestinal fistula
  • Gastrojejunal fistula
  • Gastrojejunocolic fistula
  • High-output external gastrointestinal fistula
  • Internal duodenal fistula
  • Internal gastric fistula
  • Internal gastrointestinal fistula
  • Jejunal fistula
  • Low-output external gastrointestinal fistula

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Gastrocolic fistula
  • Gastrojejunocolic fistula

Code Also

  • , if applicable, disruption of internal operation surgical wound T81.32

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Fistula(cutaneous)
      • duodenum
    • Fistula(cutaneous)
      • gastric
    • Fistula(cutaneous)
      • gastrocolic
    • Fistula(cutaneous)
      • gastroenterocolic
    • Fistula(cutaneous)
      • gastroesophageal
    • Fistula(cutaneous)
      • gastrojejunal
    • Fistula(cutaneous)
      • gastrojejunocolic
    • Fistula(cutaneous)
      • stomach

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR DIG008
Other specified and unspecified disorders of stomach and duodenum
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Gastric Fistula

    abnormal passage communicating with the stomach.

  • Stomach

    an organ of digestion situated in the left upper quadrant of the abdomen between the termination of the esophagus and the beginning of the duodenum.

Patient EducationClinical

Fistulas

A fistula is an abnormal connection between two parts inside of the body. Fistulas may develop between different organs, such as between the esophagus and the windpipe or the bowel and the vagina. They can also develop between two blood vessels, such as between an artery and a vein or between two arteries.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert K31.6 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
537.4 Gastric/duodenal fistula
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About K31.6Overview

Is K31.6 (Other diseases of stomach and duodenum) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report fistula of stomach and duodenum on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does K31.6 group to?

When fistula of stomach and duodenum is the principal diagnosis on an inpatient stay, it groups to MS-DRG 391, 392, with relative weights from 0.7796 to 1.2683 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of K31.6?

Under the General Equivalence Mappings, fistula of stomach and duodenum converts to ICD-9-CM 537.4 (gastric/duodenal fistula). The mapping is a direct match.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.